Microstructure and properties of novel developed tool steels processed by laser powder bed fusion
The large industrial interest in high-performance tools with enhanced service life combined with flexible manufacturing techniques promotes the development of new steels and their processing by additive manufacturing technologies like laser powder bed fusion (LPBF). In this work, the successful fabrication of FeCrV(Mo,W)C tool steels via LPBF is presented and the improvements with regards to the resulting properties are discussed in comparison to their as-cast counterparts.
The high cooling rates occurring during the LPBF process result in very fine microstructures composed of martensite, austenite and special carbides as detected by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). For Fe85Cr4Mo8V1C1, this combination of phases and the corresponding morphology results in a high macrohardness of 65 HRC, a superior compression strength of about 5300 MPa and a good fracture strain up to 16%. In addition, LPBF-processed FeCrMoVC shows significantly higher wear resistance in comparison to the as-cast counterpart and a conventional 1.2379 tool steel. Furthermore, potentiodynamic polarization measurements carried out in neutral 3.5% as well as in acidic 0.035% (pH = 3) sodium chloride solution displayed a significant improvement of the corrosion resistant of the LPBF specimens in comparison to the as-cast sample. The occurring corrosion mechanisms were analyzed by SEM and X-ray photoelectron spectroscopy (XPS). Concluding, laser powder bed fusion of novel high-performance steels shows a high potential for advanced tool design.